Optical systems have been used to determine chemical compositions of matters. Such optical systems include lasers which have long provided impetus to a wide range of spectroscopic investigations. The many advantages of lasers, such as their monochromaticity (ability to operate within a very narrow wavelength range), very high intensity compared to diffuse light sources, such as mercury lamps, and availability of inexpensive laser sources, are allowing many types of experiments and measurements not previously possible. Nowadays, the use of lasers in experiments or tests, such as absorbance or fluorescence measurements in chemical analysis, is routine.
Experiments or measurements based on the absorption or emission of light upon illumination of a sample by a light source have long been used to determine the nature of a sample's various components. The principle is based on the fact that given a high enough resolution for the measuring spectroscopic apparatus, every chemical component will give rise to a different absorption or emission (referred to hereinafter as fluorescence) spectrum which is a plot of the intensity of light absorbed or emitted by a sample measured at various wavelengths of the incident or emitted light. The absorption or fluorescence spectrum therefore corresponds to a fingerprint of a given chemical component, allowing its discrimination from other components present in the same sample.
Absorption or fluorescence spectroscopy has been an important technique for identification of unknown biological substances in aqueous (water-based) solutions. An absorption or fluorescence spectrum, of an aqueous solution, however, may be complicated by the fact that absorption bands of the various biological substances in the solution sometimes overlap, particularly in the case of large molecules, such as biomolecules, making assignments of their origins difficult. There is, in addition to absorption or fluorescence signals originating from a component of interest, a large amount of background noise generated by water and other constituents present in biological samples, such as blood or plasma.
Currently, a number of simple-to-operate, non-optical based analyzers for detection of certain infectious diseases, such as HIV infection, are commercially available. Examples of such analyzers are EKTACHEM DT 60, EKTACHEM 700P, REFLOTRON, AND SERALYZER. These systems allow tests to be performed in settings outside traditional laboratories, e.g., outpatient clinics, physicians' offices, and even shopping malls, schools, or churches. In addition, these systems offer the advantage of being economical, compact, lightweight, easy-to-operate, convenient, and requiring only a small amount of test sample. Some of these analyzers also have the potential for providing test accuracy precision similar to those obtained from more sophisticated analyzers used in large clinical laboratories. However, none of these commercially available analyzers are understood to be optical-based. Moreover, these systems are not suitable for analysis of a large number of samples. In addition, no such simple-to-operate system exists for detecting Hepatitis A, B or C infection.
Another drawback of available analyzers for detecting HIV infection is that they are not sufficiently sensitive and thus incapable of detecting HIV infection at the early stage of the infection. Only when the infection has occurred for some time such that the antibody or antigens of the HIV viruses in the blood sample reach detectable level, can the HIV infection be detected by conventional analyzers.
U.S. Pat. No. 5,267,152 to Yang et al. discloses an optical technique for a noninvasive measurement of blood glucose concentration using a near-infrared photodiode laser. Yang et al. determines the blood glucose concentration using an algorithm based upon the characteristic translational, vibrational and rotational motions of the molecules in the blood resulting from the excitation of the sample with a diode laser, and then comparing the optical signal from light reflected off the blood constituents with a calibration curve previously stored in the memory of a microprocessor. However, Yang et al. does not measure changes in the emission spectra of biological samples as a result of changes in the amounts of certain metabolites in the samples.
U.S. Pat. No. 5,258,788 to Furuya discloses an optical method for measuring the protein composition and concentration of the aqueous humor of the eye which, in addition to proteins, also contains blood cells. However, Furuya does not measure the emission of light by the constituents of a sample as a result of irradiation of the sample with a laser beam. Instead, it measures the scattering of incident light off the sample molecules rather than on the emission of light by the molecules themselves as a result of irradiation with a laser beam.
U.S. Pat. Nos. 5,238,810 and 5,252,493 both to Fujiwara et aL disclose an optical-based immunoassay method in which antigens or antibodies are labeled with micro-particles of a magnetic substance to form a magnetic labeled body, thus allowing determination of minute amounts of the antigen or antibody. It would be desirable if viruses could be optically detected without the use of magnetic particles.
It is therefore an object of the present invention to provide identification of a wavelength range of an excitation laser beam within which the fluorescence spectrum of the sample will provide information that can be used to detect and identify any infectious disease present in the sample. Also the present invention provides for identification of a fluorescence wavelength range within which the fluorescence spectrum of a sample will yield information that may be used to detect and identify any infectious organism contained in the sample. Also various parameters obtained from the fluorescent spectrum of a sample may be used to detect and identify any infectious disease contained in the sample. Thus the present invention provides apparatus and method for detecting HIV infection at an earlier stage when they are yet to be detectable by conventional methods.